Process for manufacture of mgcl2



Patented Jan. 15 1946 PROCESS FOR MANUFACTURE OF MgClz' Robert B. Maeuma, Niagara Falls, N. Y., as-

slgnor to The Mathleson Alkali Works, Inc., New York, N. Y., acorporation of Virginia No Drawing. Application March 28,1942,

Serial No. 436,627 p v '1 Claim. (Ci. 23-91 This invention relates toimprovements in the production of magnesium chloride, the essential rawmaterial for the production of metallic magnesium by electrolysis ofthefused chloride. The invention provides important economies, throughimprovement of chemical efllciency, in the production of magnesiumchloride and thus in th production of metallic magnesium. Moreparticularly, this invention relates to'improvements in the productionof aqueous magneslum chloride liquors by reaction between the mixedoxides of. magnesium and calcium produced by calcination of dolomite,the waste aqueous calcium chloride liquor from the ammonia soda processand carbon dioxide.

In the ammonia soda process, sodium bicarbonate and ammonium chlorideare formed bycarbonating an aqueous ammoniacal sodium chloride liquor.The sodium bicarbonate is the commercial product of the process. The am'monia, because oi its cost, must be recovered from the ammoniumchloride for cyclic re-use in the to some limited extent. The wasteliquor thus contains calcium sulphate in solution and, usually,

suspended calcium sulphate hemihydrate.

When mixed oxides of magnesium and calcium. produced for example bycalcining dolomite. are added tosuch an aqueous calcium chloride liquor.hydration does not proceed uniformly, the resulting slurry is notuniform and carbonation of the resulting slurry proceeds with relativelylow chemical'eliiciency measured in termsof magnesium chloride recoveryagainst magnesium chloride potentially available from the mixed oxidesApparently sulphates, particularly soluble sulphates, present in thewaste calcium chloride liquor from the ammonia soda process, even thoughpresent in relatively small amount, impede the hydration of the-mixedoxides produced by calcination of dolomite to an extent such thattheelectrolyte oi the desired melting point, viscosity and density.

A magnesium chloride product appropriate for the electrolysis can beproduced i'rom this waste liquor containing sulphates.

then add the resulting mixture of calcium hydrate and magnesium oxide tothe calcium chloride Once this limited hydration is complete, thesoluble sulphates present in the waste calcium chloride liquor arewithout efiect and a smooth and uniform slurry is rapidly and easilyformed from the mixture of Such operation, however, involves dilutionoithe magnesium chloride liquor ultimately formed to the extent thatsuch water is added for hydration.

However, the waste calcium chloride liquor from the ammonia soda processalso contains sulphates, particularly calcium sulphate. In, conventionalpractice, the temperature of the liquor in the de- To avoid suchdilution, I add sufflcient barium chloride or other soluble barium saltto an appropriately limited portion of the waste calcium chloride liquorto precipitate sulphates present,

- then hydrate the mixed oxides with this portion form a slurry ofmixed'hydrates of magnesium and calciiun subsequently subjected tocarbonation. The precipitated barium sulphate need not be separated fromthat portion of the waste calcium chloride liquor used for hydration oithe mixed oxides prior to addition of the mixed oxides since thesulphates present in insoluble form, as barium sulphate, do notinterierewith the hydration. The soluble barium salt is with advantageadded to that portion of the waste calcium chloride liquor used, forhydration as an aqueous solution. The proportion of soluble barium saltshould correspond, stoichiometrically, with the proportion of solublesulphates present in this waste liquor.

In operation, for example: 100 tons per day oi dolomite may be calcinedin a rotary kiln to produce about 50 tons per day of mixed oxides andabout 69 tons per day of C02 in a gas mixture of 25% concentration. Themixed oxides may be hydrated with about 21 tons per day of a wastecalcium chloride liquor from the ammonia soda process originallycontaining about 9.2% CaCh, about 4.1% NaCl and about 0.2% CaSOr, afterprecipitation of the sulphates present as barium sulphate by theaddition of about V ton of an aqueous solution containing about 20%38.012. The mixed hydrates thus formed may then be added to about 540tons per day of waste calcium chloride liquor of the same composition,without requiring precipitation of sulphates from this portion of theliquor, to produce a slurry of mixed hydrates which is carbonated, forexample with part of the gas mixture produced in calcinaticn of thedolomite. About 42 tonsper day of carbon After separation ofprecipitated calcium cardioxide may be absorbed in this carbonation. 36

bonate, about 664 tons per day of an aqueous liquor containing about6.7% MgCl-i and about 3.4% NaCl may be produced in this manner.

When the hydration of the mixed oxides of magnesium and calcium iscarried out in accordance with my invention, the limited hydrationproceeds without difliculty, and a smooth and uniform slurry is rapidlyand easily formed from the resulting mixture of calcium hydrate andmagnesium oxide. Subsequent carbonation or this slurry of mixed hydratesis facilitated and improvedyields of magnesium chloride are recovered.

My invention involves subject matter that in some respects is similar tosubject matter disclosed in United States Patent No. 2,359,829.

I claim:

In the production of aqueous magnesium chloride liquors by carbonatingslurries of mixed hydrates of magnesium and calcium in aqueous calciumchloride liquors containing soluble sulphates, the improvement whichcomprises calcining dolomite to form mixed oxides of magnesium andcalcium, adding suiiicient of a soluble barium salt to a portion of thecalcium chloride liquor to precipitate the sulphates, hydrating themixed oxides in this portion of liquor freed from soluble sulphateslimited to form a dry mixture of calcium hydrate and magnesium oxide,and adding this mixture to another untreated portion of the calciumchloride liquor containing soluble sulphates to produce a slurry ofmixed hydrates.

ROBERT :B. MacMULLIN.

